1. Field of the Invention
The present invention relates to a technique capable of providing images having high water fastness in the formation of color images on plain paper, and particularly to an ink set comprising a liquid composition and an ink, which is suitable for use in the formation of images making good use of an ink-jet recording system, an image forming process and apparatus using this ink set, and an image formed article obtained by using these process and apparatus.
2. Related Background Art
An ink-jet recording method is a system in which recording is conducted by ejecting an ink to apply the ink to a recording medium such as paper. In particular, according to the ink-jet recording method disclosed in Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914, in which an electrothermal converter is used as an ejection-energy supply means to apply thermal energy to an ink so as to generate bubbles, thereby ejecting droplets of the ink, the formation of a high-density multi-orifice in a recording head can be realized with ease, and high-resolution and high-quality images can be recorded at high speed.
However, the conventional inks used in the ink-jet recording method generally comprise water as a principal component, and include additionally a water-soluble high boiling solvent such as glycol for the purpose of preventing drying of the inks within nozzles, clogging at orifices, and the like. When such an ink has been used to conduct recording on a recording medium, therefore, there have been brought about problems that fixing ability cannot be sufficiently achieved, and image irregularity occurs, which appears to be attributed to the uneven distribution of a filler and a sizing agent on the surface of recording paper as the recording medium. In particular, when color images are intended to form, some inks of different colors are overlapped one after another. Therefore, color bleeding and uneven color mixing have occurred at portions of boundaries between images of different colors (this phenomenon will hereinafter be referred to as "bleeding" simply), resulting in a failure to obtain satisfactory images. In order to solve such problems, Japanese Patent Application Laid-Open No. 55-65269 discloses the addition of a compound capable of enhancing penetrability, such as a surfactant, into inks as a means for facilitating fixing ability of the inks. Besides, Japanese Patent Application Laid-Open No. 55-66976 discloses the use of inks comprising a volatile solvent as a principal component. However, the former method, in which the surfactant or the like is added to the inks, has involved a disadvantage that although the penetrability of the inks into recording paper is improved, and so the fixing ability and anti-bleeding property of the inks are improved to some extent, the image density and saturation of the resulting image are lowered because coloring materials contained in the inks also penetrate deeply into the recording paper. In addition, the inks have also involved a problem that they spread in lateral directions, resulting in deterioration of edge sharpness and resolution. On the other hand, the latter method, in which the inks comprising the volatile solvent as a principal component are used, has been liable to cause clogging due to the evaporation of the solvent in a nozzle of a recording head in addition to the above-described disadvantages attendant on the former method.
In order to improve the above-described problems, there have been additionally proposed methods in which a liquid composition, which can make the quality of images better, is applied to a recording medium prior to the jetting of an ink for recording images. For example, Japanese Patent Application Laid-Open No. 63-60783 discloses a method in which after a liquid composition containing a basic polymer is applied to a recording medium, an ink containing an anionic dye is applied thereto, thereby conducting recording. Japanese Patent Application Laid-Open No. 63-22681 discloses a recording method in which a first liquid composition containing a reactive chemical species and a second liquid composition containing a compound reacting with the reactive chemical species are mixed on a recording medium. Further, Japanese Patent Application Laid-Open No. 63-299971 discloses a method in which a liquid composition containing an organic compound having two or more cationic groups per molecule is applied to a recording medium, and recording is then conducted with inks containing an anionic dye. Japanese Patent Application Laid-Open No. 64-9279 discloses a method in which after an acidic liquid composition containing succinic acid or the like is applied to a recording medium, an ink containing an anionic dye is applied thereto, thereby conducting recording. Further, Japanese Patent Application Laid-Open No. 64-63185 discloses a method in which a liquid composition, which insolubilizes dyes, is applied to a recording medium prior to application of an ink.
However, all of these methods intend to prevent feathering of images or improve the water fastness of images by the deposition of the dyes themselves. Therefore, these methods are still insufficient in the effect to prevent the above-described bleeding between inks of different colors, and moreover poor in coverability of the inks on pulp fibers in the recording paper because the dyes deposited tend to distribute unevenly on the recording paper, resulting in lowering of evenness of images, so that the quality of characters printed may be deteriorated in some cases.
Therefore, Japanese Patent Application Laid-Open No. 8-224955 has proposed that a liquid composition containing a cationic substance is used in combination with an ink containing anionic compound, thereby obtaining an image high in optical density and good in image quality and water fastness and also in color reproducibility and resistance to bleeding.
On the other hand, it is known that when inks [for example, an ink containing a coloring material at a usual concentration (hereinafter referred to as "thick ink") and an ink containing a coloring material at a lower concentration (hereinafter referred to as "thin ink")], which have the same color tone, but are different from each other in concentration of coloring material, are used in combination in order to obtain an image high in gradation, the granular feeling of the inks is improved to provide an image of higher image quality. Further, a technique for obtaining an ink-jet recorded article of still higher quality by using a thick ink containing an anionic substance, a thin ink containing an anionic substance and a liquid composition containing a cationic substance is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-48462.